What on earth was going on in the small town of Lourdes, France, in February 1858?

In a small, rocky grotto near the Gave River, a fourteen-year-old girl named Bernadette Soubirous had seen a beautiful young woman surrounded by light. Bernadette promised the lady to return each day for fifteen days. Mobs of people were gathering near the river, praying and waiting. The authorities were furious, the priests disbelieving.

"I am the Immaculate Conception," the lady told the simple peasant girl. What could it mean?